In addition to the video and audio program portions of a television program, television signals include auxiliary information. An analog television signal such as an NTSC standard television signal includes auxiliary data during horizontal line intervals within the vertical blanking interval. An example is closed caption data which is included in line 21 of field 1. Digital television signals typically include packets, or groups, of data words. Each packet represents a particular type of information such as video, audio or auxiliary information. An example of a digital television system that processes a packetized digital television signal is the DSS.TM. (Digital Satellite System) manufactured by Thomson Consumer Electronics, Inc., Indianapolis, Ind.
Whether the system is analog or digital, a video receiver processes both video information and auxiliary information in an input signal to produce an output signal that is suitable for coupling to a display device such as a kinescope. Enabling an auxiliary information display feature, such as closed captioning, causes a television receiver to produce an output video signal that includes one signal component representing video information and another signal component representing the auxiliary information. A displayed image produced in response to the output video signal includes a main image region representing the video information component of the output signal and a smaller image region that is inset into the main region of the display. In the case of closed captioning, a caption displayed in the small region provides a visible representation of audio information, such as speech, that is included in the audio program portion of a television program.
In addition to auxiliary information processing, television systems may also include a picture-in-picture (PIP) feature that, when enabled, displays a small picture (pix) representing a first video signal simultaneously with a large, or main, pix representing a second video signal. The small pix is inset into a portion of the main pix. The small pix typically changes as video information in the first video signal changes, but certain systems include a freeze feature that prevents the image in the small pix from changing. Non-video portions of the television signal such as the audio program and closed caption information are processed separately from the video and are not affected by activation of a small-pix freeze feature.